Sleeves of thin walled polymeric materials are frequently used to protect articles, particularly those having a tubular or otherwise regular elongated configuration. Another use for such sleeves is to seal the joint between links of pipe or other conduit. Of particular utility for these purposes are heat-recoverable sleeves, i.e., sleeves that possess the property of being able to shrink to a smaller diameter when heated. Such a sleeve is constructed with a diameter large enough so that it can be conveniently placed about a substrate whereupon it is heated causing it to shrink and closely conform to that substrate.
Materials suitable for making heat-recoverable sleeves are well known. In Cook U.S. Pat. No. 3,086,242, the disclosure of which is incorporated herein by reference, there is described a variety of suitable materials obtained by crosslinking, particularly by radiation, organo polymeric precursors.
Sleeves of relatively small diameter are conveniently made by extrusion directly from the aforementioned materials. However, such is not the case with sleeves of large enough diameter to be used to cover sections of a pipe that might be employed in pipelines for the transmission of oil or gas over long distances. Because of this difficulty, it has been the practice in the past to employ so-called "wrap around" sleeves in combination with large diameter pipe. Sleeves of this type are made by wrapping a length of heat-recoverable material about the substrate, for example, a joint between two links of pipe, and joining its ends by a mechanical means that prevent the ends from separating when the sleeve is subjected to heat to occasion its recovery. Wrap around sleeves have the added advantage of not requiring access to a free end of the substrate in order to accomplish installation. Examples of such sleeves are described in the following U.S. patents, the disclosures of which are incorporated by reference:
Conde: No. 3,379,218 PA1 Ellis: No. 3,455,326 PA1 Wilson: No. 3,530,898 PA1 Muchmore: No. 3,542,077 PA1 Tanaka: No. 3,574,313
In Evans et al, U.S. Pat. No. 3,770,556, a method of making a wrap around sleeve is described in which the ends are overlapped and a contact adhesive is disposed between the overlapping ends to hold them together prior to recovery of the sleeve. Optionally, a layer of material can be applied to outside of the wrap around sleeve to prevent peelback. This layer, which can be a laminate of glass cloth and polyethylene, is also adhered to the sleeve by means of the contact adhesive.
The technique of using a contact adhesive, though quite useful, suffers from the drawback that a solvent based adhesive must be applied in the field by brushing, spraying, rolling or dipping and then permitted to dry to a relatively tack free film prior to placing the sleeve around the pipe to be covered if the sheet material is cut to size in the field. If applied at the factory, the material must be cut to a predetermined length thus limiting the range of sizes available. Furthermore, in many instances, the sleeve material has a coating of a mastic or adhesive which is used to improve the contact of the sleeve with the substrate and fill any voids. If this is the case, the mastic must be removed from the end of the sheet which is to be overlapped at the joint if the sleeve is fabricated in the field. This can be a time consuming task as well. Thus, it can be seen, that there remains a need for a simple method of making joints and wrap around sleeves for field installation.